Many applications have a need to measure position with high resolution and accuracy, but at a low cost. One example of such an application is paper motion control in inkjet printers. The spacing between nozzles in an inkjet printer is very fine—typically 1/600″ (about 1.6 mils, or 42 microns). In order to prevent visible banding when printing graphic images, the linefeed error must be significantly less than the distance between adjacent nozzles. An inkjet printer typically uses a DC servo system for motion control, with an incremental optical encoder for position feedback.
Typically, position measurement solutions require a trade-off among the factors such as resolution, cost and computing overhead. Low resolution physical components may be used and computing overhead kept low by utilizing additional circuitry, thereby increasing overall system cost. Alternatively, more costly high resolution physical components may be used, obviating the need for additional circuitry while keeping computing overhead low. In yet another solution, low resolution physical components and minimal additional circuitry may be used, resulting in higher computation overhead.
As such, there is a need for an apparatus and method for measuring position with a high resolution and accuracy. In particular, there is a need for position measurement with high resolution and accuracy, at relatively low cost, with minimal computational overhead in a system employing such a measurement apparatus.